From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 07C01386C39; Tue, 21 Jul 2026 19:35:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784662543; cv=none; b=PV+JVEJuzw9wAmCmOhEQ4weJvQX6JCu6q02L1EAQmcK/9US5Ci6nd15lB2DhptxpAHfI2RykTPGFrTC2+SLpQKu1U0fC4Mu3zjU+RhL+2msBYyi/wii+HGS2XQhlmPiwBvKZj2TGlavD95PHVXTsHW1jjJz15UZzyRKls+oDYHE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784662543; c=relaxed/simple; bh=V7GxGMHEPD3Jcpvgo9KUtDUsIpj1EJBsFaQJ0PwXCY8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ciU5Qcc9wi/W9jAl5tpCmFKrH6OoXBcvi3Ww8eiAE2LQe+zbbvpSov5sz474AUxyHxXW+1xhHjTxjCmUsuyjgUXPFJYcHz66zl/FlkxDKTFU3CFt3vMgfRxVTY+r41kSNMr1G5E1C+uhS3H8ymh5DhgpJyAm6v2Syc7edtyGl24= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mpRnTxNh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="mpRnTxNh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 240671F000E9; Tue, 21 Jul 2026 19:35:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784662541; bh=K8r6389Cbwcje20r92GAoBT70zZKiebzpQNK0eLfOhA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mpRnTxNhLZalxdC/D5dDoMSe1IOuDydVrqDQeQPzPhdkAsnTTQaS7phsKIAk45pfX YFAIlng7YUhXWOifoyP7jMeglEGVucoew9LcTeRdIaETppzOQMsIUPk8HARlLyf4e1 lEJALK9RvXBbeR0azAz/lnkmPtW+d8dpFK7eUwMM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chuck Lever , Trond Myklebust , Sasha Levin Subject: [PATCH 6.12 0484/1276] xprtrdma: Close lost-wakeup race in xprt_rdma_alloc_slot Date: Tue, 21 Jul 2026 17:15:27 +0200 Message-ID: <20260721152456.936078175@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152446.065700225@linuxfoundation.org> References: <20260721152446.065700225@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chuck Lever [ Upstream commit 765bde47fe7f197dabeb12da76831f40d0b20377 ] xprt_rdma_alloc_slot() and xprt_rdma_free_slot() lack serialization between the buffer pool and the backlog queue. A buffer freed after rpcrdma_buffer_get() finds the pool empty but before rpc_sleep_on() places the task on the backlog is returned to the pool with no waiter to wake, leaving the task stuck on the backlog indefinitely. After joining the backlog, re-check the pool and route any recovered buffer through xprt_wake_up_backlog(), whose queue lock serializes with concurrent wakeups and avoids double-assignment of slots. Because xprt_rdma_free_slot() does not hold reserve_lock, the XPRT_CONGESTED double-check in xprt_throttle_congested() is ineffective: a task can join the backlog through that path after free_slot has already found it empty and cleared the bit. Avoid this by using xprt_add_backlog_noncongested(), which queues the task without setting XPRT_CONGESTED, so every allocation reaches xprt_rdma_alloc_slot() and its post-sleep re-check. Fixes: edb41e61a54e ("xprtrdma: Make rpc_rqst part of rpcrdma_req") Signed-off-by: Chuck Lever Signed-off-by: Trond Myklebust Stable-dep-of: e786233d2e0b ("xprtrdma: Decouple req recycling from RPC completion") Signed-off-by: Sasha Levin --- include/linux/sunrpc/xprt.h | 2 ++ net/sunrpc/xprt.c | 16 ++++++++++++++++ net/sunrpc/xprtrdma/transport.c | 15 ++++++++++++++- 3 files changed, 32 insertions(+), 1 deletion(-) diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h index 81b952649d35e3..af35131d8d710d 100644 --- a/include/linux/sunrpc/xprt.h +++ b/include/linux/sunrpc/xprt.h @@ -389,6 +389,8 @@ struct rpc_xprt * xprt_alloc(struct net *net, size_t size, unsigned int max_req); void xprt_free(struct rpc_xprt *); void xprt_add_backlog(struct rpc_xprt *xprt, struct rpc_task *task); +void xprt_add_backlog_noncongested(struct rpc_xprt *xprt, + struct rpc_task *task); bool xprt_wake_up_backlog(struct rpc_xprt *xprt, struct rpc_rqst *req); void xprt_cleanup_ids(void); diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c index 09f245cda5262a..18ec0763ca21cd 100644 --- a/net/sunrpc/xprt.c +++ b/net/sunrpc/xprt.c @@ -1663,6 +1663,22 @@ void xprt_add_backlog(struct rpc_xprt *xprt, struct rpc_task *task) } EXPORT_SYMBOL_GPL(xprt_add_backlog); +/** + * xprt_add_backlog_noncongested - queue task on backlog + * @xprt: transport whose backlog queue receives the task + * @task: task to queue + * + * Like xprt_add_backlog, but does not set XPRT_CONGESTED. + * For transports whose free_slot path does not synchronize + * with xprt_throttle_congested via reserve_lock. + */ +void xprt_add_backlog_noncongested(struct rpc_xprt *xprt, + struct rpc_task *task) +{ + rpc_sleep_on(&xprt->backlog, task, xprt_complete_request_init); +} +EXPORT_SYMBOL_GPL(xprt_add_backlog_noncongested); + static bool __xprt_set_rq(struct rpc_task *task, void *data) { struct rpc_rqst *req = data; diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c index ca079439f9cceb..61706df5e485ac 100644 --- a/net/sunrpc/xprtrdma/transport.c +++ b/net/sunrpc/xprtrdma/transport.c @@ -511,7 +511,20 @@ xprt_rdma_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task) out_sleep: task->tk_status = -EAGAIN; - xprt_add_backlog(xprt, task); + xprt_add_backlog_noncongested(xprt, task); + /* A buffer freed between buffer_get and rpc_sleep_on + * goes back to the pool with no waiter to wake. + * Re-check after joining the backlog to close that gap. + */ + req = rpcrdma_buffer_get(&r_xprt->rx_buf); + if (req) { + struct rpc_rqst *rqst = &req->rl_slot; + + if (!xprt_wake_up_backlog(xprt, rqst)) { + memset(rqst, 0, sizeof(*rqst)); + rpcrdma_buffer_put(&r_xprt->rx_buf, req); + } + } } /** -- 2.53.0